The present invention relates to a packaging machine and method for continuously producing sealed packages or pourable food products from a tube of packaging material.
Many pourable food products, such as fruit juice, pasteurized or UHT (ultra-high-temperature processed) milk, wine, tomato sauce, etc., are sold in packages made of sterilized packaging material.
A typical example of such a package is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is formed by folding and sealing laminated strip packaging material. The laminated packaging material comprises layers of fibrous material, e.g. paper, covered on both sides with heat-seal plastic material, e.g. polyethylene; and, in the, case of aseptic packages, the side of the packaging material eventually contacting the food product in the package also has a layer of barrier material, e.g. an aluminium sheet, which is in turn covered with a layer of heat-seal plastic material.
As is known, such packages are made on fully automatic packaging machines, on which a continuous tube is formed from the web-fed packaging material; the web of packaging material is sterilized on the packaging machine itself, e.g. by applying a chemical sterilizing agent, such as a hydrogen peroxide solution, which, after sterilization, is removed, e.g. vaporized by heating, from the surfaces of the packaging material; and the web of packaging material so sterilized is maintained in a closed sterile environment, and is folded and sealed longitudinally to form a vertical tube.
The tube is filled continuously from the top with the sterilized or sterile-processed food product, and is sealed by pairs of jaws and then cut along equally spaced cross sections to form pillow packs, which are then folded mechanically to form the finished, e.g. parallelepiped-shaped, packages.
Packaging machines of the above type are known, e.g. from EP-A-0 887 273, which comprise two forming chains defining respective endless paths and in turn defined by a number of articulated jaws and counterjaws respectively; and the two paths have respective substantially straight branches facing and parallel to each other, between which the tube of packaging material is fed, and along which the jaws cooperate with the corresponding counterjaw is to grip and heat seal the tube at a number of successive transverse bands.
The face of each jaw comprises an induction heating element defining two straight, elongated, active surfaces, which interact with and heat the tube material to the sealing temperature, and extend on opposite sides of and parallel to an intermediate plane perpendicular to the tube axis. In place of a heating element, each counterjaw has two pressure pads made of plastic material and which cooperate wish the respective active surfaces of the heating element on the corresponding jaw.
The pillow packs so formed are separates at a cutting station downstream from the forming chains and comprising two counter-rotating rollers, one with a number of knives. Alternatively, packaging machines are known, e.g. from C-A-592747, U.S. Pat. No. 3,300,944 and EP-A-992431, in which the knives are incorporated in the jaws; and, in EP-A-992431, in particular, the cutting operation may advantageously be performed prior to the sealing operation.
The above solutions provide for producing packages at an extremely fast output rate and of adequate quality and reliability.
The extent to which the output rate of such packaging machines can be increased; however, is determined by how long the heating element of each jaw must be held contacting the tube material to achieve complete sealing of the packaging material.
It is an object of the present invention to provide a packaging machine designed to eliminate the above restriction.
According to the present invention, there is provided a packaging machine for producing sealed aseptic packages of a pourable food product from a tube of packaging material fed along a vertical path and filled continuously with said food product, said machine comprising:
gripping means for gripping said, tube at equally spaced cross sections; and
sealing means for sealing the packaging material of said tube along said cross sections;
and being characterized in that said sealing means comprise a first and a second sealing device forming part of respective distinct, successive units of said machine; said first sealing device interacting with said cross sections for a time shorter than the time required to achieve complete sealing of the cross sections, but sufficient to form respective temporary aseptic transverse sealing bands; and said second; sealing device interacting with said temporary sealing bands to seal them completely.
The present invention also relates to a method of producing sealed packages of a pourable food product from a tube of heat-seal sheet packaging material, fed along a vertical path and filled continuously with said food product, said method comprising the steps of:
gripping said tube at equally spaced cross sections; and
sealing the packaging material of said tube along said cross sections;
and being characterized in that said sealing step comprises a first and a second sealing operation performed successively on distinct units of a packaging machine for producing said packages; said first sealing operation being performed along said cross sections for a time shorter than the time required to achieve complete sealing of the cross sections, but sufficient to form, respective temporary aseptic transverse sealing bands; and said second sealing operation being performed to finally seal said temporary sealing bands.